Disable checksum offload

alopez@ac.upc.edu · 07-18-2012, 10:57 AM

Hi everyone,

I would like to disable the checksum offload of my network card. I have found this command that should solve my problem:

ethtool -K eth0 tx off rx off

When I query the status of the network card with ethtool -k eth0 everything seems ok, but when I use wireshark, the TCP packets have errors in the checksum. The connectivity is ok so I suppose that the checksum offload is not disabled.

rx-checksumming: off
tx-checksumming: off

I am using Ubuntu 12.04

Thanks in advance

jefro · 07-18-2012, 11:21 AM

I forget what the condition was when checksum was always on. Maybe the same checksum value for ever frame? Is each packet reporting the checksum wrong in wireshark or just some or many?

I guess restarting network can't hurt to try.

A very slim chance the board can't change for some reason.

Unplug ethernet cable and wait a few seconds and plug back in.

alopez@ac.upc.edu · 07-18-2012, 01:23 PM

Thanks for your answer. I have noticed that the only packet that wireshark detects with a wrong packet are SYN packets and ACK packets of TCP connections. Any reason for this behaver?

jefro · 07-18-2012, 03:50 PM

I assume you have this checked and/or you looked at packet info for the bad checksum. http://wiki.wireshark.org/TCP_Checksum_Verification

Then some issue with those two. Either some alternate syn checksum, firewall deal or vpn deal is all I can guess.

Checksum offloading reports all frames as bad as I recall in wireshark.

Hopefully someone knows for sure.